Nakatani is visiting Hawaii for meetings with high-ranking U.S. officers. The U.S. plan to deploy the land-based Terminal High Altitude Area Defense system in South Korea has drawn objections from China and North Korea.Citing the THAAD and other U.S. defense systems, Nakatani told reporters, "We want to speed up our study of advanced activities and equipment of the United States."

Adoption of the technology by Japan could also agitate China, which has criticized Prime Minister Shinzo Abe’s bid to strengthen the role of Japan’s military, and chill a nascent recovery in ties between Asia’s two biggest economies. Abe told President Barack Obama last week that he supported U.S. naval patrols to assert free navigation in the South China Sea, where China has built artificial islands as a platform to assert its claims to more than 80 percent of the waters.

The Thaad issue has left South Korean President Park Geun Hye caught between the U.S, which maintains more than 28,000 troops in the country to defend against North Korea, and China, its biggest trading partner and ally in efforts to resolve historical and territorial disputes with Japan.

North Korea on Nov. 15 declared a no-sail zone off its eastern coast, suggesting the country may be preparing to test-launch a missile in the sea that lies between the Korean peninsula and Japan, according to Yonhap News. The test could involve a new type of proprietary ballistic missile that separates into several “sub-missiles” at high altitude, the South Korean news agency reported.